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Original article
Acute hamstring injuries in Swedish elite sprinters
and jumpers: a prospective randomised controlled
clinical trial comparing two rehabilitation protocols
Carl M Askling,1,2 Magnus Tengvar,3 Olga Tarassova,1 Alf Thorstensson1
▸ Additional material is
published online only. To view
please visit the journal online
(http://dx.doi.org/10.1136/
bjsports-2013-093214).
1
The Swedish School of Sport
and Health Sciences,
Stockholm, Sweden
2
The Section of Orthopaedics
and Sports Medicine,
Department of Molecular
Medicine and Surgery,
Karolinska Institutet,
Stockholm, Sweden
3
Department of Radiology,
Karolinska University Hospital,
Stockholm, Sweden
Correspondence to
Dr Carl M Askling, The
Swedish School of Sport and
Health Sciences and the
Section of Orthopaedics and
Sports Medicine, Department
of Molecular Medicine and
Surgery, Karolinska Institutet,
GIH Box 5626 Stockholm
114 86, Sweden;
carl.askling@gih.se
Received 22 October 2013
Revised 15 January 2014
Accepted 31 January 2014
ABSTRACT
Background Hamstring strain is a common injury in
sprinters and jumpers, and therefore time to return to
sport and secondary prevention become of particular
concern.
Objective To compare the effectiveness of two
rehabilitation protocols after acute hamstring injury in
Swedish elite sprinters and jumpers by evaluating time
needed to return to full participation in the training
process.
Study design Prospective randomised comparison of
two rehabilitation protocols.
Methods Fifty-six Swedish elite sprinters and jumpers
with acute hamstring injury, verified by MRI, were
randomly assigned to one of two rehabilitation
protocols. Twenty-eight athletes were assigned to a
protocol emphasising lengthening exercises, L-protocol,
and 28 athletes to a protocol consisting of conventional
exercises, C-protocol. The outcome measure was the
number of days to return to full training. Re-injuries were
registered during a period of 12 months after return.
Results Time to return was significantly shorter for the
athletes in the L-protocol, mean 49 days (1SD±26, range
18–107 days), compared with the C-protocol, mean
86 days (1SD±34, range 26–140 days). Irrespective of
protocol, hamstring injuries where the proximal free
tendon was involved took a significantly longer time to
return than injuries that did not involve the free tendon,
L-protocol: mean 73 vs 31 days and C-protocol: mean
116 vs 63 days, respectively. Two reinjuries were
registered, both in the C-protocol.
Conclusions A rehabilitation protocol emphasising
lengthening type of exercises is more effective than a
protocol containing conventional exercises in promoting
time to return in Swedish elite sprinters and jumpers.
INTRODUCTION
To cite: Askling CM,
Tengvar M, Tarassova O,
et al. Br J Sports Med
2014;48:532–539.
Acute hamstring injury is common in track and field
athletes, especially in elite sprinters and jumpers.1–7
Furthermore, hamstring injuries are a heterogeneous
group consisting of different injury types, locations
and sizes, which makes recommendations regarding
rehabilitation and prognosis about healing time difficult.8–14 The reinjury rate is high,15–17 which may
indicate inadequate rehabilitation programmes and/
or premature return to sports.18 19
There is a lack of clinical research and consensus,
based on prospective, randomised studies, regarding the effectiveness of various rehabilitation protocols for acute hamstring injuries in elite sprinters
and jumpers. Overall, few studies until now have
evaluated the effectiveness of different treatment
protocols for acute hamstring injuries in any type
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
of sport.20 21 However, recently a study on
Swedish elite football players showed that a protocol aimed at loading the hamstrings during extensive lengthening mainly during eccentric muscle
actions was significantly more effective compared
with a conventional protocol in promoting time to
return to play after acute hamstring injury.13 It is
not possible to generalise these results to other elite
athletes in different sports, with a different
training-process and with other demands on the
hamstring muscle group without performing the
same protocol in a new clinical trial. The current
investigation uses the same methodological
approach as the study on elite football players.13
Aim
The main objective of this study on Swedish elite
sprinters and jumpers was to compare the effectiveness of two rehabilitation protocols for acute
hamstring injuries with varying emphasis on
muscle-tendon lengthening by evaluating time
needed to return to full participation in the training
process. Other aims were to study possible associations between injury type, location, size, palpation
pain and time to return.
MATERIAL AND METHODS
Swedish male and female elite sprinters and
jumpers were enrolled using our extensive contacts
with medical teams and coaches working with elite
track and field athletes in Sweden. These athletes
were juniors (between 15 and 19 years) and seniors
(20 years and older) ranked among the top 20 in
each discipline indoors and/or outdoors. Also, the
Swedish Athletic Association took part by informing all major track and field clubs in Sweden about
the study. The total recruitment time was
38 months, January 2009–February 2012. Forty-six
sprinters and 10 jumpers (of whom 8 were horizontal jumpers) were included, all with clinical
signs of acute hamstring injury, as confirmed by
MRI. A randomisation process was used to assign
athletes to either of the two protocols, the
L-protocol or the C-protocol, respectively. Athletes
were stratified into subgroups according to gender,
injury type (ie, sprinting-type or stretching-type
injury) and proximal free tendon involvement or
not (see below). The first athlete in each stratified
subgroup was randomised to either the L-protocol
or C-protocol using a dice. Subsequent athletes in
each subgroup were then alternated between protocols. The allocation of each athlete in a subgroup
was therefore dependent on the randomised allocation of the first athlete in that subgroup. In
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Original article
addition, eight sprinters and jumpers with clinical signs of acute
hamstring injury, but where the MRI showed no sign of injury,
were followed in parallel. These MRI-negative athletes were all
assigned to the L-protocol. The use of non-steroidal antiinflammatory drugs (NSAIDs) and/or other pain reducing medicine during the rehabilitation period was not allowed. All athletes gave their informed consent prior to participation.
Approval of the study was granted by the Regional Ethics
Committee (Dnr: 2008/1320-31/2). There were no dropouts in
the study.
extension and straps stabilising the upper body and the contralateral leg, was performed. The instruction to the athlete was to
perform a straight leg raise as fast as possible to the highest
point without taking any risk of injury (three trials per leg,
uninjured leg tested first; no warm-up). If the athlete experienced any insecurity during this voluntary straight leg raising
(on a Visual Analogue Scale, from 0 to 10), he/she was not
allowed to go back to full training. Instead, the rehabilitation
period was extended and the H-test repeated with an interval of
3–5 days until insecurity was eliminated.
Inclusion/exclusion criteria
MRI
To be included, the athlete had to have sustained acute sudden
pain in the posterior thigh that immediately forced the athlete
to stop the activity, training or competing. The initial clinical
examination had to reveal localised pain when palpating the
hamstring muscles, localised pain when performing a passive
straight leg raise test, and increased pain when adding an isometric hamstring contraction during that test.8 Exclusion criteria
included verified or suspected earlier hamstring injury in the
same leg during the past 6 months, extrinsic trauma to the posterior thigh, ongoing or chronic low back problems and
pregnancy.
All athletes underwent an MRI investigation within 5 days after
the acute injury. MRI investigations were performed on a 1.5
Tesla superconductive MRI unit (Magnetom Symphony,
Siemens, Erlangen, Germany). Briefly, longitudinal, sagittal and
frontal short tau inversion recovery (STIR) images as well as
transversal T1-weighted and STIR images (5 mm slice thickness
and 0.5 mm gap) were obtained from both legs.9 All MRI investigations were assessed and reported by one of the radiologists
(MT). A muscle was considered injured when it contained highsignal intensity (oedema) on the STIR images, as compared with
the uninjured side. If more than one muscle/tendon was injured,
the one with the greatest signal abnormality was considered the
‘primary’ injury and the second largest, the ‘secondary’ injury.
In this study, MRI parameters were quantified only for the
primary injury. The free proximal tendon (PT) was deemed
injured if 2 of the 3 following parameters were present: the
tendon was thickened, and/or had a collar of high-signal intensity around it, and/or had high intratendinous signal intensity, as
compared with the uninjured side. The maximal longitudinal
length of the muscle/tendon oedema was measured.9 In addition, the perpendicular distance between the level of the most
proximal pole of the oedema and the level of the most distal
part of the ischial tuberosity was measured.9
Injury situation—type of injury
At the first visit, the athletes were interviewed by the same
test-leader (CMA) about the injury situation, that is, the movements or exercises at which the acute injury occurred, whether
it was during a training session or competition. In addition, the
type of injury was established, that is, sprint-type injury, happening at high-speed running9 12 or stretch-type injury, occurring
during slow stretching to extreme muscle lengths.10 11
Clinical examination
All athletes were examined within 2 days after the injury. The
clinical examination included manual assessment of flexibility
and strength of the injured and uninjured leg. The uninjured leg
was always tested before the injured leg, and flexibility before
strength. Flexibility was measured with a passive straight leg
raise test (until the athlete reported pain and/or discomfort) and
a standard flexometer.8 The isometric strength test was performed with the athlete in a prone position with resistance
applied at the heel at 15° and 45° of knee flexion. The strength
was tested manually by performing a combined knee flexion
and hip extension due to the bi-articular nature of the hamstring
muscles. Hamstring strength was also tested in a lengthened
state in a supine position with the knee positioned at 15° of
flexion while resistance was applied to the heel. The foot was
maintained in plantar flexion in order to limit the activation of
the gastrocnemius muscle. A bilateral comparison was performed for each measurement.
The point of peak palpation pain was recorded and the
distance between that point and the ischial tuberosity was measured.8 The same test-leader (CMA) performed this clinical
examination weekly until there were no signs of injury remaining. The decision by the test-leader (CMA) that there were no
signs of injury remaining had to be confirmed by an independent colleague by performing the same clinical examination.
Specific rehabilitation protocols
The time from the date of injury to the date of rehabilitation
protocol initiation was 5 days for both protocols. Overall, exercises were chosen that could be performed in any place and
without the use of advanced equipment. The exercises of the
L-protocol specifically aimed at loading the hamstrings during
extensive lengthening, mainly during eccentric muscle actions. In
contrast, the C-protocol consisted of conventional exercises for
the hamstrings with less emphasis on lengthening. Each rehabilitation protocol consisted of three different exercises, where exercise 1 was aimed mainly at increasing flexibility, exercise 2 was a
combined exercise for strength and trunk/pelvis stabilisation and
exercise 3 was more of a specific strength training exercise.13 All
exercises were performed in the sagittal plane. The intensity and
volume of training were made as equal as possible between the
two protocols. The training sessions were supervised, at least
once every week, during the whole rehabilitation period, and the
speed and load were increased over time. No pain provocation
was allowed at any time when performing the exercises. All exercises included in the two rehabilitation protocols are explained in
figures 1–6. Video demonstrations of all six exercises (L-protocol
and C-protocol) showing how the progression can be performed
are included as supplemental files.
Askling H-test
When the clinical examination at the end of the rehabilitation
showed no signs of injury remaining, the Askling H-test was
performed.22 A simplified version of the H-test, without an electrogoniometer but with a knee brace to keep the leg in
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General rehabilitation programme
A general rehabilitation programme with a subject-specific progression was followed by all athletes in both specific protocols.
The general programme was implemented by the test-leader
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
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Original article
Figure 1 L-1 ‘The Extender’: the
player should hold and stabilise the
thigh of the injured leg with the hip
flexed approximately 90° and then
perform slow knee extensions to a
point just before pain is felt. Twice
every day, 3 sets with 12 repetitions
(see online supplementry video 1).
Figure 2 L-2 ‘The Diver’: the exercise
should be performed as a simulated
dive, that is, as a hip flexion (from an
upright trunk position) of the injured,
standing leg and simultaneous
stretching of the arms forward and
attempting maximal hip extension of
the lifted leg while keeping the pelvis
horizontal; angles at the knee should
be maintained at 10–20° in the
standing leg and at 90° in the lifted
leg. Owing to its complexity, this
exercise should be performed very
slowly in the beginning. Once every
other day, three sets with six
repetitions (see online supplementry
video 2).
Figure 3 L-3 ‘The Glider’: the
exercise is started from a position with
upright trunk, one hand holding on to
a support and legs slightly split. All
the body weight should be on the heel
of the injured (here left) leg with
approximately 10–20° flexion in the
knee. The motion is started by gliding
backwards on the other leg (note the
low friction sock) and stopped before
pain is reached. The movement back to
the starting position should be
performed by the help of both arms,
not using the injured leg. Progression
is achieved by increasing the gliding
distance and performing the exercise
faster. Once every third day, three sets
with four repetitions (see online
supplementry video 3).
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
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Figure 5 C-2 Cable-pendulum: A stationary cable-machine or
expander is used. With the uninjured leg as the standing leg, forward–
backward hip motions are performed with the injured leg with the
knee in approximately 20–30° flexion. This exercise involves the whole
body and should be performed slowly in the beginning of the
rehabilitation period. Once every other day, three sets with six
repetitions (see online supplementry video 5).
Figure 4 C-1 Stretching—contract/relax. The heel of the injured leg is
placed on a stable support surface in a high position (close to
maximum) with the knee in approximately 10° flexion. The heel is
pressed down for 10 s and then, after relaxation for 10 s, a new
position is assumed by flexing the upper body slowly forwards for 20 s.
Twice a day, three sets with four repetitions (see online supplementry
video 4).
Statistical analyses
(CMA) week by week and supervised by the PT responsible for
the athlete in the track and field club during the entire rehabilitation period. No pain and/or discomfort was allowed from the
injured posterior thigh during the rehabilitation process. Acutely,
the athlete should use crutches if pain was provoked by walking.
The general programme was performed three times a week
and started with stationary cycling 10 min, 10×20 s fast foot
stepping in place, 10×jogging 40 m with short strides,
10×10 m forward/backward accelerations. When the above part
of the general programme could be performed without pain
and/or discomfort, a progressive running programme was
started. This was composed of high-speed running drills 6×20,
4×40 and 2×60 m, performed three times a week.
In addition to the specific protocol and the general programme, all athletes were asked to conduct as much as possible
of their standard training programme without experiencing any
pain and/or discomfort. This training was supervised by their
regular track and field coaches.
Outcome
The main outcome was time to return, that is, time from injury
to full participation in the training process. Also, occurrence of
reinjuries was registered during a 12 month period after return.
If a re-injury occurred, the medical team responsible was to
immediately contact the study leader so that the same procedure
as for the original injury could be repeated. The full 1-year
follow-up period was completed by all athletes in the study.
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All statistical analyses were conducted with STATISTICA V.11.0
software (StatSoft Inc). The Shapiro-Wilk W tests showed that
the data were not normally distributed. A Mann-Whitney U test
was performed to investigate differences in age, height and mass
as well as MRI and palpation measures. A χ2 test was applied to
investigate differences in proportion of injury type and PT
involvement as well as in gender. The Mann-Whitney U test was
also used to assess differences in time to return between the protocols, between subgroups with respect to PT involvement (with
Bonferroni correction applied), as well as between MRI-negative
athletes and athletes with sprinting-type injury within the
L-protocol. The Mann-Whitney U test (Cohen’s d) for independent samples was applied and the χ2 test ( p) was used as a measure
of effect size. Spearman’s rank order correlations were calculated
to investigate associations between time to return and MRI and
palpation parameters. The significance level was set at p≤0.05.
RESULTS
Injury situation, type and location
Thirty (52%) of all the 56 MRI-verified injuries occurred
during competition, 14 (50%) in the L-protocol and 16 (57%)
in the C-protocol, respectively. Fifty-two (93%) of the 56 injuries were sprinting-type and 4 (7%) stretching-type injuries. In
44 of the 56 athletes (79%), the primary injury was located in
the long head of biceps femoris (BFlh) and in 7 of those 44
(16%), there was a secondary injury, in all cases located in the
semitendinosus (ST). In the remaining eight injuries of sprinting
type, the primary injury was located in the ST. In the four athletes with a stretching-type injury, the injury location was in the
semimembranosus.
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
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Original article
Figure 6 C-3 Pelvic lift: This exercise
is started in a supine position with the
body weight on both heels, and then
the pelvis is lifted up and down slowly.
Start with the knee in 90° of flexion.
The load is increased by putting more
of the body weight on the injured leg
and by having a greater extension in
the knee. Ultimately, only the slightly
bent injured leg is carrying the load.
Every third day, three sets with eight
repetitions (see online supplementry
video 6).
Characterisation of protocol participants
There were no significant differences between groups of athletes
in the L-protocol and the C-protocol with respect to age,
height, mass, gender, performance level, type of injury and
involvement of the proximal free tendon (table 1). Neither were
there any group differences in distance between the most proximal pole of the oedema and the ischial tuberosity, length of the
oedema and distance between the point of peak palpation pain
and the ischial tuberosity (table 1).
Askling H-test
Eight athletes (29%) in the L-protocol and 19 (68%) in the
C-protocol experienced insecurity when performing the H-test
and therefore needed to extend their rehabilitation period. On
average, the time to return was prolonged by 8 days (1SD±3.0,
range 3–14) in the L-protocol and by 10 days (1SD±3.5, range
4–20) in the C-protocol, respectively.
Time to return
Time to return was significantly shorter in the L-protocol compared with the C-protocol ( p<0.001, d=−1.21), mean 49 days
(1SD±26, range 18–107 days) versus 86 days (1SD±34, range
26–140 days; figure 7). Time to return was also significantly
shorter in the L-protocol than in the C-protocol for injuries not
involving and involving the PT ( p<0.01, d=−1.76 and
p<0.01, d=−2.12, respectively; figure 8). Injuries not involving
the PT showed a significantly shorter time to return than those
involving the PT in the L-protocol and C-protocol ( p<0.001,
d=−2.65 and p<0.001, d=−2.41, respectively; figure 8). Time
to return for the four stretching-type of injuries was, on
average, 121 days (range 106–140 days). Correlation analysis
showed that the shorter the distance to the ischial tuberosity
from the most proximal pole of the injury measured by MRI or
peak palpation pain, the longer was the time to return (table 2).
A longer length of the oedema was also correlated with a significantly longer time to return (table 2).
Re-injuries
There were two re-injuries registered during the 12-month
follow-up period. These re-injuries occurred in the C-protocol
88 and 120 days after the initial injury, respectively. Both
re-injuries were of sprinting-type and located in the BFlh. The
times to return for the re-injuries were 34 and 42 days as compared with 56 and 88 days for the initial injuries.
MRI-negative group
All of the eight injuries in the MRI-negative group were of
sprinting-type. The characteristics of the MRI-negative group
were similar to those of the corresponding group of 26 athletes
with MRI-confirmed sprint injuries in the L-protocol (table 3),
but had a significantly shorter time to return ( p<0.001, d=
−1.59), mean 15 days (1SD±3, range 11–19 days) versus
45 days (1SD±22, range 18–99 days; figure 9).
DISCUSSION
Effects of rehabilitation protocol
The choice of rehabilitation protocol after acute hamstring
injury can have a considerable effect on time to return to full
training in Swedish elite sprinters and jumpers. In this study, the
average time to return was 37 days shorter, 49 vs 86 days (43%)
Table 1 Descriptive, MRI and palpation data, as means±1 SD (median and range) or ratios (%) for athletes in the L-protocol and the
C-protocol, respectively
Age (years)
Height (cm)
Mass (kg)
Female (%)/male (%)
Sprinting-type (%)/stretching-type (%)
Proximal free tendon (PT) not involved (%)/PT involved (%)
Distance from proximal injury pole to ischial tuberosity (mm)
Injury length (mm)
Peak palpation pain, distance to ischial tuberosity (cm)
L-protocol (n=28)
C-protocol (n=28)
p Value (effect size)
21±4 (19, 15 to 29)
178±9 (176, 162 to 193)
71±9 (70, 53 to 86)
32/68
93/7
57/43
75±83 (65, −30 to 250)
145±85 (105, 30 to 310)
10±7 (9, 1 to 26)
19±3 (18, 15 to 29)
180±8 (181, 165 to 193)
71±10 (75, 53 to 87)
32/68
93/7
57/43
73±70 (50, −20 to 250)
149±65 (155, 40 to 295)
10±7 (7, 2 to 24)
0.167
0.520
0.890
1.000
1.000
1.000
0.864
0.520
0.994
(0.443)*
(−0.174) *
(−0.019) *
(0) †
(0) †
(0) †
(0.031) *
(−0.060) *
(0.010) *
*Mann-Whitney U test (Cohen’s d).
†χ2 test π. The level of significance was set at p≤0.05.
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
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Figure 7 Time to return, in days, in the L-protocol (n=28) and
C-protocol (n=28). The boxes represent IQRs in the boxes, the
horizontal lines represent median values and black squares represent
mean values; whiskers=mean±1 SD. *** Denotes significant difference
( p<0.001, Mann-Whitney U test).
with exercises emphasising loading of the hamstring muscles at
lengths near the maximal hamstring length (L-protocol) as compared with conventional exercises (C-protocol). Hamstring
length was probably similar in the flexibility exercises in both
protocols. A similar sized superiority of the L-protocol was
recently reported by Askling et al13 in a study on hamstring
injuries in Swedish elite football players, using the same method
as in the present study, the mean recovery times being 28 days
(range 8–58 days) and 51 days (range 12–94 days) for the
L-protocol and C-protocol, respectively.
It should be noted that included in these numbers for days to
return are additional days caused by the inclusion of an extra criterion test, the Askling H-test. On average, the rehabilitation period
was prolonged by 10 days (1SD±3.4, range 3–20 days) for the athletes and 7 days (1SD±2.7, range 3–14 days) for the football
players due to the execution of the Askling H-test.13 Without this
extra test, the time to return would have been shorter, but the difference between the L-protocol and the C-protocol would still
have remained highly significant, for example, mean 47 days vs
79 days for the athletes. It seems most likely that the requirement
of a secure H-test for everyone before being allowed to return to
full training/competition would have functioned to prevent
re-injuries. In this study, only two re-injuries occurred among the
56 athletes (3%) during the 12 month follow-up (in the footballers:
only 1 of 75).13 This is considerably lower that the recurrence rates
of 14–25% reported earlier for these types of sports.16 23 24 It is
worth noting that should the hamstring injury recur, the second
injury is usually more severe than the first, typically requiring a
longer time away from sport than the original one.16 23 24
The exercises in the L-protocol and C-protocol were selected
based on practical experience. This includes a number of exercises, joint excursions and speed. Progression was steered by the
avoidance of pain. Considering the lack of objective data, we
have chosen to describe the protocols in quite some detail for
the readers/users to form their own opinions. It is our belief
that the rather remarkable difference in outcome between the
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Figure 8 Time to return, in days, for athletes with injuries either
involving or not involving the proximal free tendon (PT) in the
L-protocol (n=12 and 16, respectively) and the C-protocol (n=12 and
16, respectively). The boxes represent IQRs; in the boxes, the horizontal
lines represent median values and black squares represent mean
values; whiskers = mean±1 SD. **p<0.01; ***p<0.001 denote
significant differences (Mann-Whitney U test).
two protocols is mainly due to the more systematic attempts to
put load on the hamstrings during maximal dynamic lengthening in the L-programme, involving movements at the hip and
the knee. Otherwise, the two protocols were made as similar as
possible in terms of early start after injury, thorough instruction
and regular follow-up and progression in load/speed/excursion
based on the avoidance of the pain criterion.
It is proposed that neuromuscular inhibition of hamstring voluntary activation occurs following acute hamstring injury, and
that this inhibition has a negative effect on hamstring recovery
by limiting hamstring load during lengthening exercises.18 19
This limited exposure to eccentric stimuli at long hamstring
muscle lengths could potentially lead to eccentric hamstring
weakness and selective hamstring atrophy, possibly in combination with selective hypertrophy of the short head of biceps
femoris,18 resulting in a shift in the torque–angle relationship.19
The L-protocol used in the present study was aimed to stress the
injured hamstrings from day five after injury occurrence and
during the entire rehabilitation process. One possible explanation of the positive result of the L-protocol could be that the
type of exercises included in the protocol was beneficial to voluntary activation of the injured hamstrings compared with the
C-protocol.
Effects of factors not related to rehabilitation protocol
Earlier investigations have demonstrated that the type of injury,
involvement of the free muscle tendon, location of pain and
injury in relation to the ischial tuberosity and the size (length)
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Table 2 Correlations between time to return and MRI and
palpation parameters in players in the L-protocol and the
C-protocol, respectively
Distance to ischial
tuberosity (mm)
Length (mm)
Palpation (cm)
L-protocol
Spearman’s r
p Value
C-protocol
Spearman’s r
p Value
−0.895
<0.001
−0.896
<0.001
0.851
−0.885
<0.001
<0.001
0.662
−0.775
<0.001
<0.001
Significant (p≤0.05) correlations are in italics.
of the injury are important factors associated with the duration
of the time to return.8–13 The current study showed that
increased recovery time can be expected with peak palpation
pain closer to the ischial tuberosity, MRI documented involvement of the free muscle tendon, oedema closer to the ischial
tuberosity and longer overall oedema length. Time to return to
sport (average 15 days) for the MRI-negative group was clearly
the shortest. This is in accordance with earlier studies demonstrating that MRI-negative cases have better prognosis for recovery than those showing injury signs on MRI.13 14 There were
too few stretching type of injuries (4 of 56) to allow a statistical
comparison, but actual times to return for athletes with stretching mechanisms were all longer than the longest for the sprint
injuries. Otherwise, the data confirmed earlier findings from
sprinters, dancers and a group of athletes from different sports
as well as from football players.8–13 A notable difference was
that the injury length was smaller and its distance to tuber
longer in the current athletes than in the football players despite
a longer time to return.13 One factor that may explain the
longer time to return to sport for sprinters and jumpers compared with football players is that in order to prevent re-injury
elite sprinters and jumpers probably need 100% restored function, but an elite football player can possibly play again without
100% restored function. This indicates that such associations
should preferably be made within the same category of sport.
Finally, a couple of additional practical observations concerning the injury situation and training layout might be worth highlighting. Almost half, 26 of 56, of the injuries occurred during
training sessions, about equally distributed between the two protocols: 14 (50%) in the L-protocol and 12 (43%) in the
C-protocol, respectively. The athletes witnessed that a clear
majority (20; 77%) of these injuries happened at the very end
of a training session with high-speed drills, typically during the
last of a total of 10 planned repetitions of 120 m sprints to
maximal speed. Of the four stretching-type of injuries, all
Figure 9 Time to return, in days, for MRI-negative athletes (n=8, all
performing L-protocol) and for athletes with sprinting-type injuries
within the L-protocol (n=26). The boxes represent IQRs; in the boxes,
the horizontal lines represent median values and black squares
represent mean values; whiskers=mean±1 SD. *** Denotes significant
difference ( p<0.001, Mann-Whitney U test).
occurring during initial warm-up, two happened when the
coach manually applied force to make the athlete reach a more
extreme movement excursion in a unilateral straight leg raise.
Strengths and weaknesses
Following the initial clinical examination and the MRI investigation, the test-leader (CMA) randomised the athletes to the
L-protocol or C-protocol, respectively. One of the authors
(CMA) was responsible for supervising all athletes’ rehabilitation
protocols once a week and also for performing the clinical
examinations and the Askling H-test. This provided consistency
for instructions, examinations and testing. However, it prevented blinding and increased the risk of bias. To decrease bias,
an independent, blinded test leader had to verify absence of
clinical injury signs before the Askling H-test. Furthermore, the
performance in this test was judged by the athlete in terms of
absence of insecurity. Finally, it needs to be pointed out that the
cohort consisted of elite athletes eager to perform well and
return to sport as soon as possible.
Table 3 Descriptive data, as means±1 SD (median and range) or (%) for players in the MRI-negative group and the group of athletes with
only sprinting-type injury within L-protocol, respectively
Age (years)
Height (cm)
Mass (kg)
Female (%)/male (%)
Sprinting-type (%)/stretching-type (%)
MRI-negative (n=8)
L-protocol (n=26)
p Value (effect size)
20±3 (20, 17 to 24)
177±10 (182, 162 to 186)
70±9 (73, 55 to 80)
25/75
100/0
21±4 (19, 15 to 29)
179±9 (176, 162 to 193)
71±9 (71, 53 to 86)
27/73
100/0
0.984
0.563
0.765
0.914
(−0.169)*
(−0.195) *
(−0.152)*
(0.002)†
*Mann-Whitney U Test (Cohen’s d).
†χ2 test (Phi ϕ). The level of significance was set at p≤0.05.
Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
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Original article
CONCLUSIONS
2
A rehabilitation protocol consisting of mainly lengthening type
of exercises is more effective than a conventional protocol in
promoting return to full training in Swedish elite sprinters and
jumpers after acute hamstring injury. On this basis, it is recommended that hamstring injury rehabilitation protocols should be
preferentially based on strength and flexibility exercises that primarily involve high loads at long muscle-tendon lengths.
Further studies are needed to verify the possible role of applying
the Askling H-test to reduce the commonly high rate of recurrence of hamstring injury.
3
4
5
6
7
What are the new findings?
8
A rehabilitation protocol consisting of mainly lengthening type
of exercises is more effective than a conventional protocol in
promoting return to full training after acute hamstring injuries in
Swedish elite sprinters and jumpers.
9
10
11
How might it impact on clinical practice in the near
future?
▸ Improve rehabilitation efficiency after acute hamstring injury
by using protocols with lengthening exercises.
▸ Improve prognosis by using palpation and MRI to establish
injury pain, location, tissues involved and size.
12
13
14
15
16
Acknowledgements The authors thank the Swedish Athletic Association and the
medical staff and coaches in the Swedish elite track and field clubs, who sent
athletes to be included in the study. The authors also thank Hans Larsson,
Sabbatsberg Sjukhus, Toni Arndt, The Swedish School of Sport and Health Sciences
and Ulf Gustafsson, FeelGood for their skilful contributions to this research. The
Swedish Centre for Sport Research is gratefully acknowledged for financial support.
Contributors CMA, MT and AT designed the study. CMA, MT, OT and AT
monitored the data collection, analysed the data and drafted and revised the paper.
Funding This study was supported by grants from the Swedish Centre for Sport
Research, grant number FO2012-0045.
Competing interests None.
17
18
19
20
21
22
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
23
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Askling CM, et al. Br J Sports Med 2014;48:532–539. doi:10.1136/bjsports-2013-093214
Downloaded from http://bjsm.bmj.com/ on March 4, 2015 - Published by group.bmj.com
Acute hamstring injuries in Swedish elite
sprinters and jumpers: a prospective
randomised controlled clinical trial
comparing two rehabilitation protocols
Carl M Askling, Magnus Tengvar, Olga Tarassova and Alf Thorstensson
Br J Sports Med 2014 48: 532-539
doi: 10.1136/bjsports-2013-093214
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